EFFECTS OF MIXING DIVERSE ORGANISMS 277 



larger amount of yolk present Is rapidly consumed. Thus 

 when the young fish is ready to swim about, the yolk has 

 been absorbed and does not interfere with swimming. In 

 the smaller heteroclitus embryos the circulation is slower. 

 When the large majalis egg is fertilized by heteroclitus, 



Figure 56. Development of a hybrid between a larger species of fish, 

 Fundulus majalis, and a smaller species, Fundulus heteroclitus, after 

 Newman (1908). A, egg of Fundulus majalis; B, egg of Fundulus 

 heteroclitus. C, young hybrid developing on the large egg of majalis. 

 D, young hybrid at the time that it should begin to swim about; 

 there still remains a large mass of egg yolk, which prevents success- 

 ful swimming, so that the hybrid dies. 



the young hybrid develops up to a certain stage. But in the 

 hybrid the blood circulation is slower than in the pure 

 majalis, owing to the crossing with the slower heteroclitus. 

 The result is that the yolk is only slowly absorbed, so that 

 when the young fish is ready to swim about, it is still bur- 

 dened with a mass of yolk (figure 56, D). It attempts to 



